Myoglobin Structure and Function

Myoglobin (Mb) is a structurally complex molecule that binds and stores oxygen inside of skeletal and cardiac muscles cells.

A large, coiled polypeptide called globin makes up most of the molecule.

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In a hydrophobic pocket formed by two of the globin’s folds is a heme group. The heme consists of an atom of ferrous iron (Fe2+) and a surrounding porphyrin ring (= four nitrogen-containing pyrrole molecules.

Two histidine molecules are associated with the heme. On one of the sides of the heme is the proximal histidine, which binds the Fe2+ of the heme to the nearby globin. It helps stabilize the position of the attached heme.

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The distal histidine, which is not bound to the heme, helps prevent oxidation of Fe2+ to Fe3+. Oxygen does not bind to Fe3+.

The distal heme also reduces carbon monoxide’s (CO) affinity for heme, which makes it easier for O2 to bond.